The present invention relates to logic monitors and more particularly to a delayed latch strobe generator which may be used in such monitors.
Among the techniques which have been developed for monitoring the operation of digital logic circuits, the most basic technique is to simply check voltages one test point at a time. Since digital information is often processed in parallel, the circuit being monitored may have to be cycled through its operating sequence a number of times by an operator to monitor all of the points required to establish the value of parallel-presented digital information.
Permanent and portable monitors have also been used for displaying the status of particular logic circuits. Such monitors are special purpose units; i.e., units which may be used only with a particular set of logic circuits. Since special purpose monitors must be newly designed each time the digital logic is altered, such monitors are relatively costly.
To overcome the disadvantages associated with the prior art monitors, a general purpose digital logic monitor was invented. This monitor is described in detail in the U.S. application Ser. No. 640487 filed Dec. 15, 1975 and assigned to the assignee of the present invention.
The monitor disclosed therein is a hand-held unit which may be electrically connected to a number of test points in the circuit being serviced through a ribbon cable. The unit has a visual numeric display showing the value of signals on those test points. The monitor includes means for allowing an operator to generate auxiliary clock signals which step a circuit being serviced through its operating sequence. The monitor also includes means for generating a latch strobe so that the data appearing on the numeric display can be fixed at the discretion of the user.
Where the digital logic system is part of a control for an electromechanical device, such as an automatic mailing machine, normal latch strobes may be generated either on a time basis or upon the occurrence of readily detected events; e.g., the movement of a letter past a photosensitive detector. However, the user may be interested in monitoring data at other times. Heretofore, the user guessed when the right time was at hand and manually generated a latch strobe to freeze the numeric display. Clearly, this approach does not allow a user to consistently and accurately obtain the desired information.